Benefits of Low Electron-Affinity Material as the N-Type Layer for Cu(In,Ga)S2 Solar Cell

Abstract

Despite the potential in single- and multi-junction solar cells application, research into the wide band gap CuIn1−xGax(Se1−ySy)2 or CIG(SSe)2 solar cell material, with Eg≥1.5eV, has yet to be extensively performed to date. In this work, we conducted a numerical study into the role of the n-type layers in CIG(SSe)2 heterojunction solar cells, specifically concerning the maximum open-circuit voltage of the devices. In the first part of the study, we derived a new ideal open-circuit voltage equation for a thin-film heterojunction solar cell by taking into account the current contribution from the depletion region. The accuracy of the new equation was validated through a simulation model in the second part of the study. Another simulation model was also used to clarify the design rules of the n-type layer in a wide band gap CIG(SSe)2 solar cell. Our work stressed the importance of a positive conduction band offset on the n-/p-type interface, through the use of a low electron affinity n-type material for a solar cell with a high open-circuit voltage . Through a precise selection of the window layer material, a buffer-free CIG(SSe)2 design is sufficient to fulfill such conditions. We also proposed the specific roles of the n-type layer, i.e., as a passivation layer and selective electron contact, in the operation of CIGS2 solar cells.

Growth of Zn‐Ge‐O Thin‐Film as a Transparent Conductive Oxide Buffer Material for Chalcopyrite Solar Cell

“…[ 13 ] In our previous work, we have theoretically demonstrated the importance of positive band offset at the n‐ and p‐type layers interface to achieve a high open circuit device. [ 14,15 ] This work was in line with previous experimental work by other researchers on alternative n‐type material couplers for chalcopyrite such as ZnS, [ 16 ] (Zn, Mg)O, [ 17 ] or Zn(S, O) [ 18 ] that also underlined the role of band alignment in improving chalcopyrite solar cell performance. [ 19–21 ]…”

“…As discussed in our previous work on the optimum conduction band offset design, [ 14,15 ] a flat or positive band offset (i.e., spike structure) at the p–n‐interface of chalcopyrite solar cell will improve the performance of the solar cell device. Based on Equation (1), the optimum band offset will be formed by a film with 4.6% Ge‐content.…”

Development of n-type Zn(O, S) buffer layer deposited by open-air CVD method for Cu(In, Ga)Se2 solar cells

“…[8][9][10][11][12] It has been reported that the CdS buffer layer suppresses sputtering damage on the CIGS surface during a transparent conductive oxide (TCO) deposition, 13) reducing shunt paths, 14) and improving current density-voltage (J-V ) characteristics by improving conduction band alignment. [15][16][17] However, due to its narrow E g of 2.42 eV, light with a wavelength shorter than 512 nm is absorbed by CdS, causing a decrease in a quantum efficiency and resulted in a loss of a short-circuit current (J SC ). Additionally, CdS buffer is concerned with an environmental burden owing to the use of a toxic cadmium element.…”